Titanium alloy

ABSTRACT

This invention relates to a titanium alloy and, more particularly, to such an alloy having strength and fracture toughness, even when hot, formed by virtue of the use of aluminum, vanadium, zirconium, and cobalt.

United fiates Patent Heitman 1 Mar. 14, 1972 [54] TITANIUM ALLOY3,113,227 12/1963 Bomberger et al. ..75/i75.5

[72] inventor: George H. Heitman, Shrewsbury, Mass. FOREIGN PATENTS ORAPPLICATIONS [731 Assigml wymn'cm'dm 90mm, Gram, Mass- 782,564 9/1957Great Britain ..75/175.5 [22] Filed: June 2, 1969 810,949 3/1959 GreatBritain ..75/l75.5 848,905 9/1960 Great Britain ..75/l75.5 [21] Appl.No; 829,725

Primary ExaminerCharles N. Lovell v 52 us. ca ..75/17s.5 Niamey-NormanBlodsefl [51] Int. Cl ..C22c 15/00 [58] Field ofSearch ..75/175.5;148/32, 32.5, 133 [5 ABSTRACT This invention relates to a titanium alloyand, more particu- [56] References cued larly, to such an alloy havingstrength and fracture toughness, UNITED STATES PATENTS even when hot,formed by virtue of the use of aluminum,

vanadium, zirconium, and cobalt. 2,754,204 7/1956 Jaffee et al..75/l75.5 2,868,640 1/1959 Butler ..75/ 175.5 4Claims, No DrawingsTITANIUM ALLOY BACKGROUND OF THE INVENTION There has recently beenconsiderable interest in the development of new and betterhigh-strength, deep-hardening alloys. This has come about with thedesign of larger airframe and deep submergence structural parts oftitanium. One deephardening alloy which is commercially available is analloy of titanium with 13% vanadium, 11% chromium, and 3% aluminum.Another common alloy for this purpose is the one containing titaniumwith 6% aluminum, 4% vanadium, and 2% tin; this alloy shows highstrength capability, but the strength decreases significantly in crosssections over 1 inches and above 3 inches only annealed properties areobtained. The U.S. Pat. to Butler No. 2,868,640 describes an alloy oftitanium with 3-10% aluminum, 5% vanadium, l% zirconium, and 05%molybdenum; tests show that this alloy is not as strong as could bedesired. Furthermore, these alloys have the disadvantage that they losetheir strength when they are made into parts by hot forming methods.These and other deficiencies of the prior art alloys have been obviatedin a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide atitanium alloy having deep-hardening characteristics.

Another object of this invention is the provision of an alloy havingrelatively high strength in thick sections with good ductility andfracture toughness.

A further object of the present invention is the provision of an alloysystem combining strength and fracture toughness (in air and in saltwater) in sections up to at least 4 inch in thickness.

It is another object of the instant invention to provide alpha and betatitanium alloys of 170 to 175 Ks.i. ultimate strength range which,nevertheless, have good elevated-temperature tensile strength, andnotched tensile strength.

A still further object of the invention is the provision of a titaniumalloy having use as a hot-forming high-strength material, since itretains its strength after exposure to temperatures in the range from1200 to 1300 F.

It is a further object of the invention to provide a titanium alloysystem which maintains its strength after exposure to a very hightemperature, so that it is useful for hot formed elements.

With the foregoing and other objects in view, which will appear as thedescription proceeds, the invention resides in the combination andarrangement of steps and the details of the composition hereinafterdescribed and claimed, it being understood that changes in the preciseembodiment of the invention herein disclosed may be made within thescope of what is claimed without departing from the spirit of theinvention.

SUMMARY OF THE INVENTION In general, the invention has to do with adeep-hardening titanium alloy containing about 6% aluminum, 4 to 7%vanadium 1 to 4% cobalt, 4% zirconium, and the remainder titanium. Morespecifically, about 6% vanadium is used and 2 or 3% cobalt. DESCRIPTIONOF THE PREFERRED EMBODI- MENT The invention consists, in the preferredembodiment, of an alloy of titanium with 6% aluminum, 6% vanadium, 2%cobalt, and 4% zirconium. Vanadium may be used in the range from 4 to7%, and satisfactory results are obtained when the amount of cobalt liesin the range from 1 to 4%.

EXAMPLES A nominal composition was selected for evaluation in theAl-V-Co-Zr alloy system, i.e., Ti 6Al-6V-2Co-4Zr. One lbs. heat of thealloy was made. The chemical composition and beta transus temperaturesare reported in Table 1.

TABLE 1 Chemical Analysis and Beta Transus Temperatures V Cc Fe C

a-i-BIB Transus TABLE II Heat treat study on titanium alloy with cobaltaddition, upset forged below the beta transus 200. 1,500 F (2)AC+1,000 FAC 205 208. 1,500 F AC-i-l, 208. 212. 1,500 F (2)AC+1,150 F (4)AC 188.193. 1,500 F.(2)AC+1,200 F.(4)AC 180. 182. 1,500" F.(2)AC+1,250 F.(4)AC176. 181. 1.500 F.(2)WQ+1,100 F.(4)AC 206. 208. 1,300 F.(4)AO 155. 168.1,475 F.(2)AC+1,200 F.(4)AC 160. 168. 1,475 F (2)AO+1,250 F. AC 161.172. 1,475" F (2)AC+1,300 F )AC 150. 162. 1 500 F (2)AC+1,300 F (4)AC167. 172. 1,450 F (2)AC+1,300 F (4)AC 161. 163.

1,500 F.(2)AC+900 F.(4)AC 225. 230.

1,500 F.(2)AC+950 F.(4)AC 225. 232. 1,350 F. 4)A 157. 160. 1,425F.(2)AC+1,300 F.(4)AC 164. 166. 1,400 F. )AC 158. 160.5 1,475F.(16)AC+1,250 F.(4)AC 169. 175.0 1,650 F.(2)AC+1,250 F.(4)AC 177. 188.51,475 F (B)AC+1,250 F (4)AC 170. 175.0 1,47 F (4)AC+1,250 F 175. 185.51,700 F (2)AC+1,250 F (4)AC 177. 185.0 1,600 F (2)AC+1,250 F )AC 173.181.5 1 AC+900 F (24)AC 214. 220.0

3 In the balance of this specification, the Ti 6Al6V-2Co-4Zr will bereferred to as Ti 6-6-2-4.

The ingot was received in the form of 8 inches d1 element approximately12 inches long. The ingot was initially upset at 1,550" F. (25%) andthen drawn out. The drawn billet was recrystallized at l,650 F. (abovethe beta transus) and from that temperature upset 25%. After the secondupsetting, the forging was drawn out to 4 inches square with severalwash heats of 1550 F. A section of the 4 inches square, 2-1/2 incheslong was cut from the end of each heat and upset into a pancake 0.55inches thick. The upsets were cut into tensile blanks and heat treatedat various solution temperatures and aging cycles. The results of theinitial heat treat study is reported in Table II.

would be helpful for hot forming operations. All of the tests taken arein the longitudinal direction and results are reported in Tables Illthrough V.

While it will be apparent that the illustrated embodiments of theinvention herein disclosed are well calculated adequately to fulfill theobjects and advantages primarily stated, it is to be understood that theinvention is susceptible to variation, modification, and change withinthe spirit and scope of the subjoined claims.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:

l. A deep hardening titanium alloy, consisting of a. 4 to 6% aluminmn,

b. 4 to 7% vanadium, v

TAB LE I11 Tensile properties of T1 GAl-GV-ZOo-4Zr 4' square, heattreated Test remit. 0.2% as. U.T.S. EL, 3A., Location (K s.l.) (K s.l.)percent percent J Long Surface 4 Q7 m. ggg g g 1 g gig Average 166. 7176. 13. 2 28. 1 Long center v$ R T P6. 4 112.3 e 0 33.1 I 65.0 m. .o .2

Average j 165. 7 171. s 14. o as. 0 Long mid section 41$ 500 130. o 154.s 16. o 35.1 129. 0 151. 1e. 5 35.1

Average 129. 5 15s. 0 1e. 2 as. 7 I Long mid section 4'51? 9m o ilA 2.2.s .s

Average 86. 4 101. 1 43. 0 74. 6

From the initial heat treat results on the Ti 6624 alloy: TABLE IV TableII, two heat treatments (Test Nos. 19 and 33 in Table I1) appeared tohave relatively high strength with good ductility. The two heattreatments were evaluated on fir-inch upset forging and were air cooledfrom the solution treating temperature. Because of the larger sectionsize of the billet (4 inches square), the first solution treatment wasfollowed by a water quench to allow maximum response during aging. The 4inch square billet (approximately inches long) was solution treated atl,475 F.(2)WQ and aged 1,250" F.(4)AC. Two transverse tensiles weretaken from the center of the 4 inch square 2-;6 inches from the end. Theresults of the two tensiles are as follows:

The results established the composition of Ti 6-6-2-4 to be apotentially deep hardenable alloy.

A section of the 4 inch square billet was cut 7 inches long and solutiontreated at t,600 F.(2)AC. with aging cycle of l,250 F.(4)AC. Twolongitudinal bend tests were machined from the center of the 4 inchsquare and two longitudinal bend tests were machined from the surface.The tensile properties and fracture toughness are as follows:

Long Surface 165.8

Notched strength and fracture toughness of Ti 6Al-6V2Co4Zr, 4' square,heat treated l,600 F.(2)AC+1,260 F.(4)AC HTABLE v Stress rupture of TiGAHlV-2Co-4Zr 4' square, heat treated 1,600" F.(2)AC+1,250 F.(4)AC "V"notch stress rupture 70 F.

K51. 180 K51. K31. 200 K 5.1. (hrs.) (his) (his) (hrs) Lonimid section4':

are

c. l to 4% cobalt, d. 3 to 5% zirconium, and e. the remainder titanium.2. An alloy as recited in claim 1, wherein 2% cobalt is used. 3. Analloy as recited in claim 1, wherein 4% zirconium is used.

4. An alloy as recited in claim 1, wherein 6% vanadium is used.

t t t

2. An alloy as recited in claim 1, wherein 2% cobalt is used.
 3. Analloy as recited in claim 1, wherein 4% zirconium is used.
 4. An alloyas recited in claim 1, wherein 6% vanadium is used.